# '''[[FDTD_Source_Types#Gaussian_Beam_Source|Gaussian Beam Source]]''': A distributed source with a complex-valued focused Gaussian beam profile defined using a virtual box object enclosing the entire physical structure.
A lumped source is the most commonly used way of exciting a structure in [[EM.Tempo]]. A lumped source is an ideal source that must be placed on a line object that is parallel to one of the three principal axes and shows up as a small red arrow on the host line. Lumped sources are typically used to define ports and compute the port characteristics like S/Y/Z [[parameters]].
Waveguide source is used to excite the dominant TE<sub>10</sub> mode of a hollow rectangular waveguide. Waveguide sources typically provide more accurate results for scattering [[parameters]] of waveguide structures compared to lumped sources as they represent the actual dominant propagating modes at the transmission line ports. A plane wave source is another popular excitation method that is used for calculation of the radar cross section of targets or reflection and transmission characteristics of periodic surfaces.